A conventional industrial robot is as shown, for instance in FIG. 2. One end of a first arm B is coupled to a base A in such a manner that it is swingable, the other end of the first arm B is coupled to one end of a second arm C in such a manner that the second arm C is swingable. Furthermore, the other end of the second arm C is coupled to a wrist mechanism D in such a manner that the latter D performs a bending operation swinging about an axis perpendicular to the longitudinal axis of the second arm C, and a revolving operation revolving around the longitudinal axis. The wrist mechanism D is coupled to an end effector E comprising a holding device and a machining device.
The wrist mechanism D which is coupled to the end of the arm of an industrial robot, and perform a biaxial operation including a bending operation and a revolving operation is as shown in FIG. 3, and has been disclosed (for instance by Japanese Patent Unexamined Publication No. Sho. 63-185595.
In FIG. 3, reference numeral 1 designates a hollow cylindrical arm; 11, a stationary gear box coupled to the end of the arm 1; and 2, a hollow cylindrical bending drive shaft which is supported in the arm 1 through bearings 12. The end portion of the bending drive shaft 2 is formed into spline teeth 2A. Reference numeral 21 designates a first bevel gear. which has spline grooves 2B in the inner cylindrical surface which are engaged with the spline teeth 2A. The first bevel gear 21 is supported by bearings 22 which are held between the first bevel gear 21 and the stationary gear box 11. The bearings 22 are secured to the arm 1 and the first bevel gear 21 with a bearing retainer 22a and a nut 22b.
Further in FIG. 3, reference numeral 3 designates a revolving drive shaft supported in the drive shaft 2 through bearings 23, and its end portion has spline teeth 3A; 31, a second bevel gear having spline grooves which are engaged with the spline teeth 3A of the revolving drive shaft 3. The second bevel gear 31 is supported by bearings 24 which are fixedly held between the second bevel gear and the stationary gear box 11 with a bearing retainer 32 and a nut 33.
Reference numeral 4 designates a bending drive speed reducer whose stationary portion is secured to the stationary gear box 11. The bending drive speed reducer 4 has an input shaft 42 and an output member 43 which are coaxially turned around an axis which is perpendicular to the direction of axis of the bending drive shaft 2. A third bevel gear 44 engaged with the first bevel gear 21 is fixedly secured to the input shaft 42, while a movable gear box 45 is secured to the output member 43.
Reference numeral 5 designates a first intermediate bevel gear which is turned around the same axis as the output member 43 of the speed reducer 4, and is engaged with the second bevel gear 31. The first intermediate bevel gear 5 has a spur gear 51 mounted on its axis, and is supported by bearings 14 through a housing 13 secured to the arm 1. Reference numeral 15 designates a bearing which supports the movable gear box 45 to allow the housing 13 to perform a bending operation. Reference numeral 6 designates a second intermediate bevel gear which is supported to a movable gear box 45 in parallel with the first intermediate bevel gear with the aid of bearings 46, and is secured to a spur gear 61 which is engaged with the spur gear 51. Reference numeral 7 denotes a revolving speed reducer, and its stationary section 72 is secured to the movable gear box 45 so that its input shaft 71 is coaxial with the revolving drive shaft 3. A fourth bevel gear 73 engaged with the second intermediate bevel gear 6 is secured to the input shaft 71, and an end effector 8 is secured to an output member 74.
In the above-described prior art, the second bevel gear 31 is supported, in a cantilever mode, to the stationary gear box 11 by means of the bearings 24, while torque is transmitted from the revolving drive shaft 3 to the second bevel gear 31 by the engagement of the spline teeth 3A of the revolving drive shaft 31 with the spline grooves 3B of the bevel gear 3. Hence, there is a radial gap between the revolving drive shaft 3 and the second bevel gear 31.
Therefore, the supporting portion of the second bevel gear 31 is decreased in rigidity, which produces vibration or noise, or lowers transmission efficiency.
In the case where the second bevel gear 31 is supported, in a cantilever mode, in the stationary gear box 11, in order to prevent the decrease of rigidity thereof, it is necessary to provide a number of bearing fixing components such as a sleeve and a nut, which makes it difficult to reduce the manufacturing cost.
Furthermore, in the prior art, the revolving drive shaft 3 is supported through the bearings 23 in the bending drive shaft 2. Hence, it is necessary to support the bending drive shaft 2 in the arm 1 through the bearings 12, thereby to increase the rigidity of the bending drive shaft 2, which increases the number of bearings.
The first bevel gear 21 is supported by the bearings 22 which are fixed to the arm 1 and the first bevel gear 21 with the bearing retainer 22a and the nut 22b; that is, it is supported in a cantilever mounted mode, and the number of components is increased.